U.S. patent number 5,343,782 [Application Number 07/936,994] was granted by the patent office on 1994-09-06 for anti-flare method using offgoing slip speed and rate of change of slip-speed to determine pressure compensation for incoming clutch.
This patent grant is currently assigned to General Motors Corporation. Invention is credited to Fereydoon Jamzadeh.
United States Patent |
5,343,782 |
Jamzadeh |
September 6, 1994 |
Anti-flare method using offgoing slip speed and rate of change of
slip-speed to determine pressure compensation for incoming
clutch
Abstract
In a computer-based control, pressure is progressively decreased
in an off-going clutch for gradual release while pressure is
progressively increased in an on-coming clutch. Positive off-going
clutch slip and the rate of slip change are monitored to detect the
onset of turbine flare. A control calculates a compensation
pressure which is added to the on-coming clutch pressure to reduce
the slip and thus the flare. The control calculates a term
proportional to slip and an integral term when the slip and slip
rate are positive. When the slip rate goes negative, the control
calculates a negative integral term. All the calculated terms are
combined to produce the compensation pressure value.
Inventors: |
Jamzadeh; Fereydoon
(Indianapolis, IN) |
Assignee: |
General Motors Corporation
(Detroit, MI)
|
Family
ID: |
25469324 |
Appl.
No.: |
07/936,994 |
Filed: |
August 31, 1992 |
Current U.S.
Class: |
477/156;
701/58 |
Current CPC
Class: |
F16H
61/061 (20130101); F16H 2059/467 (20130101); B60W
2050/001 (20130101); F16H 2061/0477 (20130101); F16H
59/48 (20130101); B60W 2050/0012 (20130101); F16H
2059/385 (20130101); Y10T 477/6939 (20150115); F16H
2061/0078 (20130101); B60W 2050/0022 (20130101) |
Current International
Class: |
F16H
61/06 (20060101); F16H 59/38 (20060101); F16H
59/46 (20060101); F16H 59/48 (20060101); F16H
61/00 (20060101); B60K 041/02 () |
Field of
Search: |
;364/424.1
;74/866,867 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Braun; Leslie A.
Assistant Examiner: Ta; Khoi
Attorney, Agent or Firm: Navarre; Mark A.
Government Interests
The invention herein described was made in the course of work under
a contract or subcontract thereunder with the Department of the
Army.
Claims
The embodiments of the invention in which an exclusive property or
privilege is claimed are defined as follows:
1. In a control for an automatic transmission having a turbine
driving an output shaft through a gearset which achieves an upshift
by controllably releasing an off-going torque transmitting device
for a current speed ratio and controllably applying a fluid
operated on-coming torque transmitting device for a lower speed
ratio by a commanded on-coming pressure, wherein the turbine is
subject to flare if the on-coming pressure is insufficient when the
off-going torque transmitting device is released, a method of
controlling the turbine flare comprising the steps of:
determining a slip speed across the off-going torque transmitting
device, wherein the slip speed is a measure of flare;
calculating a rate of slip speed change;
when the determined slip speed is positive and the calculated rate
of slip speed change is positive, calculating a proportional term
based on the detected slip and a first integral term based on the
calculated rate of slip speed change;
summing the proportional and integral terms to form a compensation
term; and
correcting the commanded on-coming pressure in accordance with the
compensation term.
2. The method of controlling flare as defined in claim 1 including
the step of calculating the first integral term only when the
calculated rate of slip speed change is below a positive
threshold.
3. The method of controlling flare as defined in claim 1 including
the steps of:
calculating a second integral term based on the calculated rate of
slip speed change when the detected slip is positive and the
calculated rate of slip speed change is less than a determined
negative value; and
including the second integral term in the compensation term.
4. The method of controlling flare as defined in claim 1 wherein
the slip speed is determined periodically during a shift and
wherein the step of calculating a rate of slip speed change
comprises subtracting a previously determined slip speed from a
currently determined slip speed.
5. The method of controlling flare as defined in claim 1 wherein an
interim proportional term is calculated periodically during the
shift and wherein the step of calculating the proportional term
includes updating the proportional term in accordance with the
interim term whenever the interim term exceeds the proportional
term.
6. In a control for an automatic transmission having a turbine
driving an output shaft through a gearset which achieves an upshift
by controllably releasing an off-going torque transmitting device
for a current speed ratio and controllably applying a fluid
operated on-coming torque transmitting device for a lower speed
ratio by a commanded on-coming pressure, wherein the turbine is
subject to flare if the on-coming pressure is insufficient when the
off-going torque transmitting device is released, a method of
controlling the turbine flare comprising the steps of:
measuring turbine speed and output speed;
determining a slip speed across the off-going torque transmitting
device as the measured turbine speed less the product of the
measured output speed and the current speed ratio, wherein the slip
speed is a measure of flare;
calculating a rate of slip speed change;
when the determined slip speed is positive and the calculated rate
of slip speed change is positive, calculating a proportional term
based on the detected slip and a positive integral term based on
the calculated rate of slip speed change;
when the determined slip speed is above the first threshold and the
calculated rate of slip speed change is less than a determined
negative value, calculating a negative integral term based on the
calculated rate of slip speed change;
summing the proportional and the integral terms to form a
compensation term; and
correcting the commanded on-coming pressure in accordance with the
compensation term.
7. The method of controlling flare as defined in claim 6 wherein
the proportional and the positive integral terms are updated
periodically when the calculated rate of slip speed change exceeds
the second threshold; and
the negative integral term is updated periodically when the
calculated rate of slip speed change is below the determined
negative value.
8. The method of controlling flare as defined in claim 6 wherein
the proportional term is calculated as the product of the
determined slip and a gain factor.
9. The method of controlling flare as defined in claim 6 wherein a
trial term is calculated periodically as the product of the
determined slip and a gain factor and the proportional term is
selected as the largest periodically calculated trial term.
10. The method of controlling flare as defined in claim 7 wherein
each integral term is calculated by calculating the product of the
calculated rate of slip speed change and a gain factor and summing
such products for a series of update periods.
11. In a control for an automatic transmission having a turbine
driving an output shaft through a gearset which achieves an upshift
by controllably releasing an off-going torque transmitting device
for one gear range and controllably applying an on-coming torque
transmitting device for a higher gear range by a commanded
on-coming pressure, wherein the turbine is subject to flare if the
on-coming pressure is insufficient when the off-going torque
transmitting device capacity is reduced, a method of automatically
shifting the transmission comprising the steps of:
disengaging the off-going torque transmitting device by reducing
its pressure according to an off-going pressure command having a
progressively decreasing value to complete such disengagement;
engaging the on-coming torque transmitting device by successively
supplying it with hydraulic pressure for a predefined fill period
and thereafter controlling such pressure to effect a progressive
engagement of the same;
determining slip speed across the off-going torque transmitting
device and the rate of slip speed change;
when the slip is positive and the rate of slip speed change is
positive, calculating a term proportional to slip and an integral
term for positive slip rate;
calculating a compensation term by summing the proportional and the
integral terms; and
correcting the commanded on-coming pressure by the amount of the
compensation term.
12. The method of shifting a transmission as defined in claim 11
including the steps of:
calculating an integral term for negative slip rate when the slip
is positive and the rate of slip speed change is less than a
determined negative value; and
including the integral term for negative slip rate in the
compensation term.
Description
FIELD OF THE INVENTION
This invention relates to a method of transmission control, and
more particularly, to a method of controlling transmission upshifts
to minimize turbine flare.
BACKGROUND OF THE INVENTION
Generally, a motor vehicle automatic transmission includes a number
of gear elements coupling its input and output shafts, and a
related number of torque establishing devices such as clutches and
brakes which are selectively engageable to activate certain gear
elements for establishing a desired speed ratio between the input
and output shafts. The brake can be of the band type or disk type;
engineering personnel in the automotive art refer to disc type
brakes in transmissions as "clutches" or "reaction clutches". As
used herein, the terms "clutches" and "torque transmitting devices"
will be used to refer to brakes as well as clutches. The input
shaft is connected to the vehicle engine through a fluid coupling,
such as a torque converter, and the output shaft is connected
directly to the vehicle wheels.
In the type of transmission involved in this invention, the
clutches are fluid operated, and each develops torque capacity in
relation to the fluid pressure in its apply chamber once such apply
chamber has been filled. Shifting from one forward speed ratio to
another involves releasing the pressure supplied to an off-going
clutch associated with the current speed ratio while initiating the
supply of fluid pressure to an on-coming clutch associated with the
desired speed ratio. Shifts performed in this manner are termed
clutch-to-clutch shifts and require precise timing in order to
achieve high quality shifting.
The present invention is directed to upshifting the transmission
from a current speed ratio to a desired speed ratio which is
numerically lower than the current ratio, the speed ratio being
defined as the transmission input speed divided by the transmission
output speed. Thus, an upshift involves a pulldown or reduction of
the input speed.
The quality of an upshift depends on the cooperative operation of
several functions, such as pressure changes and the timing of
control events. One of the measures of upshift quality is turbine
flare. Turbine flare during an upshift occurs when one or both of
the following conditions are satisfied:
a) The on-coming clutch is underfilled when the off-going clutch is
released. In this case, the turbine flare starts when the off-going
clutch starts to slip, and the amount of such slip is indicative of
the degree of flare.
b) The initial on-coming clutch pressure after the fill period is
too low. In this case, the on-coming clutch does not have the
required torque capacity to hold the turbine speed or pull it down,
and the turbine flare starts during the transition from off-going
clutch to on-coming clutch.
Typically, an upshift control, whether open loop or closed loop, is
designed to manage the smooth transfer of torque from one clutch to
the other within a given time period. If the time period expires,
full pressure is applied to the on-coming clutch. If the on-coming
clutch does not already have a reasonably high pressure, the sudden
application of high pressure can have the effect of a shock as a
result of a undesirably rapid change of axle torque. Uncontrolled
turbine flare leads to such a condition.
SUMMARY OF THE INVENTION
This invention is directed to an improved upshift control which
identifies and minimizes turbine flare during upshift by
controlling on-coming clutch pressure. The slip speed across the
off-going clutch is the primary variable used to determine the
flare and correct the on-coming clutch pressure.
In the course of an upshift, the pressure on both the on-coming
clutch and the off-going clutch are varied under computer control
which develops pressure command signals for both clutches. In
particular, the off-going clutch pressure is progressively
decreased to effect clutch release, while the on-coming clutch is
applied. The on-coming pressure includes a fill pressure for
filling the respective apply chamber and a subsequent apply
pressure which progressively increases to engage the on-coming
clutch.
A control responsive to slip is used to calculate a compensation
term which adjusts the oncoming pressure command signal to
attenuate flare, should it occur. The turbine speed and the output
speed of the transmission are monitored throughout the shift and
the value of the off-going clutch slip is periodically calculated.
The change of slip between consecutive slip calculations is used as
a measure of rate of change of slip speed, or slip rate.
When the slip is positive and the slip rate is also positive but
relatively small, a term proportional to slip is produced and an
integral term is also produced by accumulating slip rate values in
consecutive program loops. The proportional and the integral terms
are added to produce the compensation term. When the flare reduces
in speed in response to the compensation term, the slip rate
becomes negative. At this point, a negative integral term is
combined with the other terms in the compensation term to thereby
reduce the compensation signal and avoid an over-correction. As a
result of the compensation, the flare is attenuated and the
on-coming clutch capacity increases gradually at a rate sufficient
to assume the full input torque before a time-out period
expires.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic illustration of a transmission, including a
computer-based control unit for carrying out the control of this
invention.
FIGS. 2, 3, 4 and 5 are flow diagrams representative of computer
program instructions executed by the computer-based controller of
FIG. 1 in carrying out the shift control of the transmission.
FIG. 6, parts (a) through (f), is a graphical illustration of
transmission parameters experienced during a number of consecutive
upshifts including turbine and output speeds, the commanded and
actual clutch pressures, output torque, off-going clutch slip and
flare compensation.
DESCRIPTION OF THE INVENTION
Referring now to the drawings, and more particularly to FIG. 1, the
reference numeral 10 generally designates a motor vehicle drive
train, including a throttled internal combustion engine 12, a
fluidic torque converter 14 comprising a pump 16 and a turbine 18,
a multiple speed fluid operated power transmission 20 schematically
represented by two speed ranges SR1 and SR2 controlled by clutches
C1 and C2, respectively. Gear shifts are accomplished by
selectively engaging and disengaging the clutches C1 and C2.
The transmission depicted here is representative of well known
transmissions having several forward ranges, say six ranges, for
example, and therefore having a larger number of clutches and speed
ratios. The two ratio model, however, is used to illustrate the
principal of the anti-flare upshift control. It is assumed then,
that initially, the clutch C1 is fully applied and the speed ratio
SR1 is functioning. The ratio SR2 is a lower ratio than SR1 and an
upshift is effected by releasing clutch C1 and applying clutch
C2.
The engine 12 is connected to the torque converter 14 via shaft 22,
the torque converter 14 is connected to the transmission 20 via
shaft 24, and the transmission 20 has an output shaft 26 coupled to
a pair of drive wheels through a final drive gearset (not shown).
The speed and torque relationships between the engine 12 and the
drive wheels of the vehicle are controlled by the fluid operated
clutches C1 and C2.
The clutches C1 and C2, as well as the torque converter 14, are
supplied by a pressure regulated hydraulic pressure source 30. The
clutches are coupled to the source 30 via solenoid control valves
32 which determine the admission or discharge of fluid to the
clutches and the clutch pressure. The operation of pressure source
30 and the solenoid operated control valves 32 is controlled by a
computer-based control unit 34 via lines 35 in response to various
input signals representative of system parameters. Such inputs
include, among others, a torque converter output shaft speed signal
Nt on line 36, a transmission output shaft speed signal No on line
38, a system supply voltage signal Vb on line 40 and an operator
range selector position signal on line 42. The input signals No and
Nt are obtained with conventional electrical transducers such as
magnetic speed pickups 44.
Internally, the control unit 34 comprises a number of conventional
devices including a microcomputer with internal clock and memory,
an input/output device (I/O) and an array of drivers. A driver is
dedicated to each solenoid control valve 32. The driver outputs are
used to energize the respective solenoid control valves. The driver
currents determine the hydraulic pressure supplied by the solenoid
control valves, with a low current yielding a low pressure and a
high current yielding a high pressure for a normally closed valve.
Accordingly, the computer control, when properly programmed, is
effective to manage the clutch pressures to effect an upshift from
SR1 to SR2 by controllably releasing the pressure in the off-going
clutch C1 and applying pressure to the on-coming clutch C2.
FIGS. 2 through 5 are flow diagrams representative of computer
program instructions, executed by the computer-based control unit
34 of FIG. 1 in carrying out the shift control technique of this
invention. In the description of the flow diagrams the functional
explanation marked with numerals in angle brackets, <nn>,
refers to blocks bearing that number.
FIG. 2 represents an executive or main loop program which directs
the sequential execution of various subroutines. Initialization
<50> designates a series of instructions executed at the
initiation of each period of vehicle operation for setting the
various timers, registers and variable values of control unit 34 to
predetermined initial values. Thereafter, the blocks 52 to 60 are
sequentially and repeatedly executed as indicated by the flow
diagram lines at a rate which, typically, may be 20 msec per
loop.
After initialization, the various input signal values are read and
conditioned for use by the microcomputer <52>. The input
signals are tested for integrity and the system operation is
monitored to diagnose any operational problems <54>. For this
purpose it is sometimes desirable to utilize more transducers,
e.g., clutch pressure sensors, to check the operation of various
system elements. Then any problems are analyzed and solutions to
overcome or otherwise deal with them are developed <56>.
After shift scheduling determines that a certain shift should occur
<57>, the clutch control block 58 analyzes the various system
input signals, develops pressure command signals for operation of
each clutch and includes a routine for upshift on-coming clutch
control. Then the command signals are conditioned to effect the
solenoid drive currents to carry out the pressure commands for
specific shift operations <60>, and the required control
signals are outputted to the drivers for the solenoid operated
control valves 32.
In FIG. 3, the routine for upshift on-coming clutch control 58' is
shown. The general approach for on-coming clutch control is to
first quickly fill the clutch by commanding a high pressure for a
brief fill time, and then, starting at a lower pressure, by
increasing the pressure at some ramp rate. If the shift has just
been initiated <62>, timers counters and parameters are
initialized including anti-flare logic parameters <64>.
Typically, only a limited time, say 1.5 sec is permitted for shift
completion; if the time expires <66>, a rapid clutch pressure
increase is commanded <68>. Once the maximum commanded
pressure has been attained <70>, the maximum pressure is
commanded and an end-of-shift flag is set <72> and the
routine is completed.
If the shift has not timed out <66>, the anti-flare logic is
applied <74> to develop, when appropriate, additional
pressure command values to increase the on-coming clutch pressure
before time-out. If the shift is still in the fill phase
<76>, the fill phase commands are executed to obtain the fill
phase pressure <78> and the on-coming clutch pressure is
commanded to be the fill phase pressure plus compensation pressure
mandated by the anti-flare logic <80>. When the shift phase
is no longer in the fill phase <76>, the open loop on-coming
clutch control routine is executed <82>.
The open loop on-coming clutch control routine 82 is shown in FIG.
4. Clutch base pressure is calculated as a function of engine
torque <84>, the torque being supplied from an engine
controller, not shown, or being determined from a table of torque
as a function of engine speed and throttle position. If the
diagnostic routine 54 does not indicate a slip problem and the
on-coming clutch slip is near synchronization <86>, the
maximum pressure is commanded and the end-of-shift flag is set
<88>; otherwise a counter is incremented <90> and the
command clutch pressure is calculated as the base pressure, plus
the product of the counter value and a constant, plus the
anti-flare logic pressure <92>. If the maximum pressure has
been reached <94>, the program goes to block 88; otherwise
the routine exits.
The anti-flare logic routine 74 generates a compensation pressure
value P which, when added to the fill pressure or the open loop
pressure for the on-coming clutch, should be sufficient to stem the
on-coming clutch slip which allows flare. The value P includes a
term P.sub.p proportional to slip S and, depending on the rate of
slip, a positive integral term P.sub.ui and a negative integral
term P.sub.di. The pressure component terms are set to zero at the
shift initiation by the block 64 and new values for the terms are
calculated during the shift as a function of the slip S. The slip S
will have been calculated in the diagnostic block 54 as S=Nt-No*SR1
which is the difference between the turbine speed and the product
of the output speed and the current speed ratio.
FIG. 5 shows the anti-flare logic routine 74. If the diagnostic
routine 54 indicates a problem with the slip value, the anti-flare
logic is not used <100>. Also, if the slip S is not above a
threshold speed C1, say 25 rpm, the pressure compensation
calculation is bypassed <102>. When slip is above the
threshold C1, the rate of slip DELTAS is calculated as the change
in slip since the previous program loop or DELTAS=S.sub.new
-S.sub.last <104>. If DELTAS is above a threshold C2
<106>, a trial proportional term is first calculated as
P.sub.x =K.sub.p *S where K.sub.p is a calibrated gain factor such
as 0.2 <108>.
To select the maximum value of the trial proportional term, as it
is calculated in successive loops, it is determined whether P.sub.p
is less than P.sub.x <110>, and if so P.sub.p is set equal to
P.sub.x <112>. In most cases of positive DELTAS, the term
P.sub.p is sufficient for pressure compensation, but where the
turbine speed is near the engine governed speed and DELTAS is
small, the proportional term alone does not provide sufficient
correction and a more robust compensation is desirable.
Accordingly, if DELTAS is less than a threshold C3, say 5 rpm
<114>, an integral term P.sub.ui is calculated as P.sub.ui
=P.sub.ui +K.sub.u *DELTAS where K.sub.u is a gain constant such as
0.1 <116>. This term is particularly effective when the
turbine flare begins near the governed speed. When the on-coming
pressure becomes sufficient to start reducing flare, DELTAS is no
longer positive <106> and new values of P.sub.p and P.sub.ui
are not generated but the last calculated value is retained.
If the turbine flare occurs due to an underfill condition, the
proportional term and integral term for positive slip difference
effectively reduces the fill time by increasing the commanding
pressure. However, when the clutch is filled, the resulting
pressure might be more than the desired pressure for turbine pull
down, resulting in a shift shock. To offset a pressure which
becomes too high, the routine assesses whether DELTAS becomes more
negative than a threshold C4, such as 25 rpm <118>. If so, a
negative integral term P.sub.di is calculated as P.sub.di =P.sub.di
+K.sub.d *DELTAS <120>. Pdi is effective to suitably reduce
the compensation pressure value P. The final step in the anti-flare
logic is to sum the proportional and integral terms to calculate
the pressure value P <122>. The value P is added to the
commanded on-coming clutch pressure in all phases of the shift, as
indicated at <80> and <92>.
FIG. 6, graphs a-f, illustrate transmission shift parameters
generated during an anti-flare logic simulation for a six speed
ratio transmission. The graphs cover a 2-3 shift, a 3-4 shift and a
4-5 shift performed in rapid sequence, covering the time period of
3.7 seconds to 7.2 seconds of the test.
Graph (a) shows the turbine speed Nt and the transmission output
speed No over the sequence of shifts. Graph (b) shows the commanded
on-coming clutch pressure P.sub.c, the actual on-coming pressure
P.sub.on, and the off-going clutch pressure P.sub.off during each
shift. The line identified as P.sub.on in one shift becomes
P.sub.off in the next shift. The transmission output torque is
displayed in graph (c). Torque oscillations occurring between
shifts are a consequence of mismatch between turbine and output
accelerations. The off-going clutch slip S is shown in two graphs,
(d) and (e). In graph (d), the slip is shown over its whole range,
both positive and negative, and in graph e only the positive values
of slip are shown and are scaled for better visibility. The graph
(f) shows the compensation pressure P and its components as
calculated by the anti-flare logic.
During the 2-3 shift, the slip S, as shown in graph (e), does not
reach the threshold C1 (25 rpm) so that no compensation pressure P
is calculated. It is apparent from graph (b) that the off-going
pressure P.sub.off is ramped down to gradually release the
off-going clutch, and the commanded pressure P.sub.c as developed
by the on-coming clutch control logic 58' causes the actual
on-coming clutch pressure P.sub.on to increase at a steady rate.
When the maximum pressure P.sub.m is commanded the on-coming
pressure P.sub.on ramps up at a higher rate. In this illustration,
the next shift begins before the full clutch pressure is
attained.
During the 3-4 shift, the commanded fill pressure P.sub.f is
clearly shown. This shift does cause the slip to exceed the
threshold C1. At that time, the proportional term P.sub.p is
immediately generated, as shown in graph (f) and the integral term
P.sub.ui is built up in steps. When the slip S starts to decrease
the anti-flare terms remain constant. The rate of slip decrease is
not sufficient to trigger the calculation of a negative integral
term. The effect of the calculated pressure P is reflected in the
commanded pressure P.sub.c at point A and in the actual pressure
P.sub.on which then increases in slope, thereby heading off a
significant pressure deficiency when the maximum pressure is
commanded. The calculated value P and its components are reset to
zero at the beginning of the 4-5 shift.
During the 4-5 shift the anti-flare logic is again invoked due to
the large slip S. The value P.sub.p is increased in several stages
and is the dominant term in the pressure value P because of the
large slip value. The integral term is not immediately calculated
because, at first, DELTAS is greater than the threshold C3; when
the integral value P.sub.ui is calculated it does not become large.
When the slip declines at a sufficient rate, the negative integral
term P.sub.di is calculated. In this instance, it too is small and
has only little effect on the total compensation pressure P. In
other circumstances, however, the negative integral term can become
very important in correctly adjusting the on-coming clutch
pressure.
It will thus be seen that the anti-flare logic is able to
compensate for low on-coming clutch pressure which results in slip
of the on-coming clutch and turbine flare to assure a shift free of
excessive shock upon timing out of the shift.
* * * * *